FastAPI is a modern, high-performance Python web framework, particularly popular for building APIs — this guide covers deploying it in production using Uvicorn as the ASGI server.
Why FastAPI Uses an ASGI Server (Not WSGI Like Flask/Django Traditionally)
FastAPI is built on ASGI (Asynchronous Server Gateway Interface), supporting native async/await for genuinely concurrent request handling — Uvicorn is the standard ASGI server implementation used to actually run FastAPI applications.
Prerequisites
- Python installed with a virtual environment set up (see How to Set Up a Python Virtual Environment Correctly)
Step 1 — Install FastAPI and Uvicorn
pip install fastapi uvicorn[standard]Step 2 — A Basic FastAPI Application
nano main.pyfrom fastapi import FastAPI
app = FastAPI()
@app.get("/")
def read_root():
return {"message": "Hello, World!"}Step 3 — Run for Development
uvicorn main:app --reloadStep 4 — Running in Production with Multiple Workers
uvicorn main:app --host 0.0.0.0 --port 8000 --workers 4Multiple worker processes let you utilize multiple CPU cores — a common rule of thumb is (2 × CPU cores) + 1, though tune based on your actual workload characteristics.
Step 5 — Create a systemd Service
sudo nano /etc/systemd/system/fastapi-app.service[Unit]
Description=FastAPI Application
After=network.target
[Service]
User=appuser
WorkingDirectory=/opt/myapp
Environment="PATH=/opt/myapp/venv/bin"
ExecStart=/opt/myapp/venv/bin/uvicorn main:app --host 0.0.0.0 --port 8000 --workers 4
Restart=always
[Install]
WantedBy=multi-user.targetStep 6 — Start and Enable the Service
sudo systemctl daemon-reload
sudo systemctl enable --now fastapi-appStep 7 — Configure Nginx as a Reverse Proxy
server {
listen 80;
server_name yourdomain.com;
location / {
proxy_pass http://127.0.0.1:8000;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_http_version 1.1;
}
}Step 8 — Add HTTPS
sudo certbot --nginx -d yourdomain.comUsing Gunicorn as a Process Manager for Uvicorn Workers (Alternative Pattern)
pip install gunicorngunicorn main:app -w 4 -k uvicorn.workers.UvicornWorkerGunicorn's mature process management (automatic worker restart, graceful reloads) combined with Uvicorn's ASGI worker class is a common production pattern, offering more operational robustness than running Uvicorn's own worker management alone.
Exploring FastAPI's Automatic API Documentation
http://yourdomain.com/docsFastAPI automatically generates interactive API documentation (Swagger UI) based on your endpoint definitions — genuinely useful for both development and as living documentation for API consumers.
Common Errors
"Address already in use" — see How to Fix "Address Already in Use" Port Binding Errors; verify no other process (including a leftover previous instance) is already bound to the port.
Continue Reading
- How to Set Up a Python Virtual Environment Correctly
- How to Deploy a Django/Flask Application with Gunicorn and Nginx
- How to Build and Secure a REST API on a VPS
Browse more articles in Programming Languages & Runtimes.
